Multimodal Plasmonic Hybrids: Efficient and Selective Photocatalysts

Abstract

Important efforts are currently under way in order to implement plasmonic phenomena in the growing field of photocatalysis, striving for improved efficiency and reaction selectivity. A significant fraction of such efforts has been focused on distinguishing, understanding and enhancing specific energy transfer mechanisms from plasmonic nanostructures to their environment. Herein we report a synthetic strategy that brings together two of the main physical mechanisms driving plasmonic photocatalysis into an engineered system by rationally combining the photochemical features of energetic charge carriers and the electromagnetic field enhancement inherent to the plasmonic excitation. We do so by creating hybrid photocatalysts that integrate multiple plasmonic resonators in a single entity, controlling their joint contribution through spectral separation and differential surface functionalization. This strategy allows us to study the combination of different photosensitization mechanisms when activated simultaneously. Our results show that hot electron injection can be combined with an energy transfer process mediated by near-field interaction, leading to a significant increase of the final photocatalytic response of the material. In this manner, we overcome the limitations that hinder photocatalysis driven only by a single energy transfer mechanism, and move the field of plasmonic photocatalysis closer to energy-efficient applications. Furthermore, our multimodal hybrids offer a test system to probe the properties of the two targeted mechanisms in energy-related applications such as the photocatalytic generation of hydrogen and open the door to wavelength-selective photocatalysis and novel tandem reactions.

Silver based photocatalysts in emerging applications

“…36 Thus, coupling Ag with acceptor species, such as semiconductors, carbonbased materials and other metals, was explored. 51 Modifying Ag with traditional catalysts, such as TiO 2 , g-C 3 N 4 , MoS 2 , and BiOCl, can prolong charge lifetime due to the efficient carrier transfer between Ag and semiconductors. [52][53][54][55] In the meantime, the LSPR effect of Ag can enable visible light harvest for photocatalytic systems and reduce the activation energy barrier for chemical reactions.…”

“…Miguel et al achieved an H 2 generation rate in excess of 60 mmol h −1 g −1 using the bimetallic Au@Ag alloy nanorods which is far beyond that of the monometallic Au nanorods (less than 40 mmol h −1 g −1 ) with similar geometries. 51 The limited inter-band damping effect and stronger surface plasmonic resonances in Ag boosted hot-electron injection rates leading to an excellent HER.…”

Plasmonic photocatalysis in aqueous solution: assessing the contribution of thermal effects and evaluating the role of photogenerated ROS

“…The model photocatalyst is formed by the electrostatic assembly of Au NRs and 5 nm TiO 2 NPs (anatase phase) onto 500 nm silica spheres (Figure 1a, S1 and experimental details in the Supporting Information (SI)), which has proven to be a reliable material for the study of the photophysical interaction between a plasmonic and a semiconductor component. 22,23 The hybrid formed with such geometry, named SiO 2 @AuNR@TiO 2 ensures a homogeneous distribution of both active components onto the inorganic substrate (Figure 1b) and the formation of a physical interface between them (Figure S2). This characteristic is of paramount importance for an efficient hot electron transfer process through which electrons with sufficient kinetic energy can traverse from the metal to the semiconductor.…”

“…Among them, the photodegradation of RhB has proven to be a reliable means to quantify the photocatalytic activity of Au-TiO 2 hybrids, allowing straightforward monitoring with simple spectroscopic techniques. 23,25 Firstly, we tested the degradation profile of RhB when exposed to high temperatures in the dark (in the absence of photocatalyst). As can be seen in Figure S4a, the organic dye remains stable when exposed to 60 °C over a prolonged period of time (8 hours), proving that the chosen model reaction cannot proceed in the dark even at macroscopic temperatures well above those expected from plasmon-induced heating (vide infra).…”

“…13,16,19,21 In our group, we have investigated the synergistic combination of plasmonic metals and wide bandgap semiconductors leading to the formation of broadband photocatalysts with enhanced activities and efficiencies. 22,23 The population of hot electrons created at the metal component upon electromagnetic excitation can be subsequently transferred to a nearby n-type semiconductor, leaving a population of hot holes at the Fermi level of the former. In this manner, an efficient separation of charges with prolonged lifetimes that can be used to drive chemical reactions is created.…”